Dendritic Regions Research Articles

Hot deformation behavior and microstructural evolution of dual phase Ni48.6 Al10.3 Co17 Cr7.5 Fe9 Ti5.8 Ta0.6 Mo0.8 W0.4 high entropy alloy

The present study reports the hot deformation behavior, microstructural evolution, and the alloying effects of refractory elements (Ta, Mo, W) in Ni48.6 Al10.3 Co17 Cr7.5 Fe9 Ti5.8 Ta0.6 Mo0.8 W0.4 (at. %) high entropy alloy (HEA). The vacuum arc melted specimens were characterized using a scanning electron microscope, X-ray diffractometer, and Differential scanning calorimetry, which revealed the two-phase structure consisting of γ′ precipitates embedded in the γ matrix. The Energy Dispersive Spectroscopy analysis in a scanning electron microscope revealed that Mo and W partitioned into the dendritic region (KMo = 1.23 and KW = 1.28) while Ta is found to be partitioned in the interdendritic region composed of mostly γ′ precipitates (KTa = 0.67). Further, the specimens were subjected to hot deformation in the 800 °C - 1100 °C temperature range at the strain rate of 0.01s−1. The maximum flow strength was around 278 MPa and 183 MPa at 1050 °C and 1100 °C, respectively. The flow behavior is correlated with the microstructure evolution, which is characterized using electron backscattered diffraction (EBSD). In the cases of hot deformation below 1000 °C, localized plastic flow in the form of shear bands developed in coarse grain microstructure, whereas fine grains evolved due to dynamic recrystallization (DRX) in the sample deformed above 1000 °C. Further, the role of refractory elements in retaining high-temperature flow strength has been discussed.

Evolution of microstructure, mechanical properties and phase stability of CoCrFeMnNi high entropy alloys

In the present study, the microstructure and mechanical properties of various CoCrFeMnNi high-entropy alloys were investigated. Analytical studies were conducted to determine the optimal chemical composition, mixing entropy, mixing enthalpy, atomic radii, valence electron concentration (VEC), dimensionless parameter, and melting point on the Co-Cr-Fe-Mn-Ni system. The microstructure of the alloys was analyzed using FESEM, XRD, and TEM. The results showed that the microstructure of all HEAs had dendritic and interdendritic regions, with secondary precipitations detected along the grain boundaries of the alloy, mainly composed of Mn and Ni. High-density dislocation structures and nano-precipitates were predominantly present in the alloy. The mechanical characteristics such as microhardness and tensile properties are conducted at room temperature. The HEA Co25Cr25Fe10Mn30Ni10 exhibited the highest average microhardness, while the Co20Cr20Fe30Mn10Ni20 HEA had the lowest mean hardness value. This significant difference of 7.2 % may be attributed to the hard phases composed of Mn and Ni. The results of the tensile experiments indicate that the Co20Cr20Fe20Mn20Ni20 alloy has the most favorable overall properties, with an ultimate tensile strength of 441 MPa. This represents a significant increase of 37.8 % compared to 20Cr20Fe20Mn20Ni20. Furthermore, the study examines the instability of the solid-solution state caused by differences in the valence electron concentrations of the constituent elements and phase stability.

Effect of Hot Isostatic Pressing on the Stellite 6 Alloy prepared by Directed Energy Deposition

The directed energy deposited (DED) alloys show higher hardness values than the welded alloys due to the finer microstructure following the high cooling rate. However, defects such as microcracks, pores, and the residual stress are remained within the DED alloy. These defects deteriorate the wear behavior so post-processing such as heat treatment and hot isostatic pressing (HIP) are applied to DED alloys to reduce the defects. HIP was chosen in this study because the high pressure and temperature uniformly reduced the defects. The HIP is processed at 1150oC under 100 MPa for 4 hours. After HIP, microcracks are disappeared and porosity is reduced by 86.9%. Carbides are spherodized due to the interdiffusion of Cr and C between the dendrite and interdendrite region. After HIP, the nanohardness (GPa) of carbides increased from 11.1 to 12, and the Co matrix decreased from 8.8 to 7.9. Vickers hardness (HV) decreased by 18.9 % after HIP. The dislocation density (10-2/m2) decreased from 7.34 to 0.34 and the residual stress (MPa) changed from tensile 79 to a compressive -246 by HIP. This study indicates that HIP is effective in reducing defects, and the HIP DED Stellite 6 exhibits a higher HV than welded Stellite 6.

Microstructure and mechanical assessment of Inconel 625 and AISI 904L dissimilar joints using high-density welding technique for pressure vessels

The dissimilar bimetallic joints of 5 mm thick Inconel 625 and AISI 904L were accomplished through the high-density fiber laser welding (LBW) process. The metallurgical investigation ensured the micro-segregation of Mo and Nb in the dendritic and inter-dendritic regions along with the formation of secondary topologically closed packed (TCP) phases. In addition to the metallurgical studies the Kernal average misorientation (KAM), Schmid factor (SF), and nucleation of the new grains were investigated through Electron backscattered diffraction (EBSD) analysis. The tensile strength opined the occurrence of failure on the 904L side, away from the weld seam ensuring that the joints have a higher strength. The notch tensile showed a higher strength of 678 ± 4 MPa in the weld zone than that of the 904L base alloy. The Charpy V notch studies showed a drastic decrease in the impact toughness with 38 ± 2 J as compared to the base alloys under sudden impact loading at room temperature (RT).

Solidification and tribological behaviors of CoCrFeNiSi0.5-(Al,Ti) non-equiatomic high entropy alloy coatings fabricated by direct laser deposition

In order to evaluate the difference in the effects of Al and Ti elements on the microstructure and tribological behaviors of CoCrFeNi-based high entropy alloy (HEA) coatings, CoCrFeNiSi0.5-(Al,Ti) non-equiatomic HEAs coatings were prepared using direct laser deposition (DLD). The phase constitution, solidification microstructure and tribological behaviors of the HEA coatings were investigated. The results indicated that CoCrFeNiSi0.5 HEA coating was composed of face centered cubic (FCC) phase with microstructure of columnar and cellular grains. The addition of Al and Ti led to a columnar-to-equiaxed transition (CET) in the HEA coatings. When only Al was added (CoCrFeNiSi0.5Al0.5), the primary phase transformed into a body centered cubic (BCC) phase (94 vol%). Additionally, Cr3Si formed in the interdendrite (ID) region, and a spinodal decomposition structure emerged in the dendrite (DR) region. Conversely, with the inclusion of Ti alone (CoCrFeNiSi0.5Ti0.5), the matrix maintained its FCC phase, but Ni16Ti6Si7 (G phase, 20.9 vol%) and Cr15Co9Si6 (15.1 vol%) were generated in the ID and DR regions, respectively. Incorporating both Al and Ti (CoCrFeNiSi0.5Al0.5Ti0.5) significantly reduced the G phase content in the ID region to 7.9 vol% and led to the formation of dispersed Fe3Al nanoparticles with an average size of 99 nm in the DR region. The CoCrFeNiSi0.5 HEA coating exhibited the lowest hardness (249 HV0.1), the highest friction coefficient (0.778), and the poorest wear resistance. For the HEA coatings containing Al and Ti, the microhardness significantly increased to over 700 HV0.1, and the friction coefficient decreased to around 0.6. However, the wear resistance of the CoCrFeNiSi0.5Al0.5 HEA coating was almost equivalent to that of the CoCrFeNiSi0.5 with a wear loss of 5.1 mg. By contrast, the HEA coatings containing Ti demonstrated notably improved wear resistance, with wear losses of only 2.2 mg and 2.4 mg for the CoCrFeNiSi0.5Ti0.5 and CoCrFeNiSi0.5Al0.5Ti0.5 HEA coatings, respectively.

Effect of Iron Content on the Pitting Corrosion Behavior of Laser-Cladded Ni-Cr-Mo Alloy Coating in a Simulated Seawater Environment

In order to study the effect of iron content on the pitting corrosion behavior of a Ni-Cr-Mo alloy coating in a simulated seawater environment, a Ni-Cr-Mo-xFe (x = 0, 5, 10, 15, 20, 25) alloy coating was prepared through laser cladding technology. These coatings primarily consist of a γ-Ni solid solution phase, with observable iron segregation in the interdendritic regions when the iron content reaches 25 wt%. After 42 days of salt spray corrosion, it was found that pitting began to appear on the surface when the iron content in the coating increased to 10 wt%. The results of electrochemical behavior revealed that the coatings with iron contents in a range of 10–25 wt% exhibited metastable pitting characteristics, and the impedance modulus decreased with the increase in iron content. Pitting corrosion occurs due to selective corrosion of the dendritic regions. When the iron content exceeds 10 wt%, the accumulation of iron in the outer layer of the passivation film would lead to an excess of cationic vacancies, and the stability of the passive film is then reduced. This study provides a reference for the control of the iron content in a Ni-Cr-Mo alloy coating when applied in marine environments.

Experimental study on the micro-mechanical parameters of Ni-based single-crystal superalloys using nanoindentation and element distribution analysis

Ni-based single-crystal superalloys are normally prepared by directional solidification. Due to different solidification sequences, Ni-based single-crystal superalloys exhibit a typical dendritic arm structure, and the element segregation in the dendritic arm can affect the high temperature mechanical properties of the alloy. Solid solution treatment has a certain extent to reduce the inter-dendritic and dendritic arm between the concentrations of the elements, thereby changing the alloy micro-nano view parameters to improve the high temperature mechanical properties of the alloy. In this study, nanoindentation experiments were carried out on the inter-dendritic and dendritic arm of the cast and solid solution samples. The micromechanical parameters were calculated. The amounts of changes in elemental concentration were discussed with the results of the energy dispersive spectroscopy and electron probe microanalysis, so as to analyse the relationship between the micromechanical parameters and the changes in elemental concentration. The results show that solid solution treatment has a significant impact on the elastic modulus, with an increase of 114.7% of the inter-dendritic region and an increase of 142.7% of the dendritic arm. However, solid solution treatment has little effect on the hardness, with no significant change in the hardness of the inter-dendritic region and an increase of 43.86% of the dendritic arm. Solid solution treatment has a more significant effect on improving the segregation behavior of Al and Co elements, with the segregation coefficients of Al and Co elements in the inter-dendritic region decreasing and increasing by 36% and 19%, and the segregation coefficients of Al and Co elements in the dendritic arm region decreasing and increasing by 29% and 34%.

Influence of Al addition on microstructure and electrochemical behaviour of CrMnFeCoNi high-entropy alloy

To develop new corrosion-resistant materials for structural applications, CrMnFeCoNiAlx high-entropy alloys (HEAs) are produced via semi-industrial induction casting. The study aimed to investigate the influence of Al content (x = 0–0.3) on both microstructure evolution and corrosion properties of the alloys. X-ray diffraction and scanning electron microscopy (SEM) analysis revealed that all the alloys exhibited a single-phase face-centered cubic structure, with dendritic (Fe, Co, Cr-rich) and interdendritic (Mn, Ni, Al-rich) regions distinguished by elemental segregations. Furthermore, the incorporation of Al atoms into the solid solution led to an increase in the lattice parameter, indicating alloy strengthening. The corrosion resistance of the CrMnFeCoNiAlx alloy improved with higher Al addition. Electrochemical polarisation tests demonstrated a slight increase in the corrosion potential (Ecorr) and a significant decrease in the corrosion current density (icorr) upon Al addition. Additionally, slower kinetics for pit nucleation (higher E'corr) were observed, particularly notable for x = 0.3. Analysis of the corroded surfaces revealed a mixed degradation mechanism, involving pitting corrosion and selective dissolution of the interdendritic zone, which decreased as the Al content of the HEA increased. These findings underscore the effectiveness of Al addition in not only enhancing the mechanical properties of the Cantor alloy through solid solution strengthening, but also improving its corrosion resistance.

Structural and functional characterization of the IgSF21-neurexin2α complex and its related signaling pathways in the regulation of inhibitory synapse organization.

The prevailing model behind synapse development and specificity is that a multitude of adhesion molecules engage in transsynaptic interactions to induce pre- and postsynaptic assembly. How these extracellular interactions translate into intracellular signal transduction for synaptic assembly remains unclear. Here, we focus on a synapse organizing complex formed by immunoglobulin superfamily member 21 (IgSF21) and neurexin2α (Nrxn2α) that regulates GABAergic synapse development in the mouse brain. We reveal that the interaction between presynaptic Nrxn2α and postsynaptic IgSF21 is a high-affinity receptor-ligand interaction and identify a binding interface in the IgSF21-Nrxn2α complex. Despite being expressed in both dendritic and somatic regions, IgSF21 preferentially regulates dendritic GABAergic presynaptic differentiation whereas another canonical Nrxn ligand, neuroligin2 (Nlgn2), primarily regulates perisomatic presynaptic differentiation. To explore mechanisms that could underlie this compartment specificity, we targeted multiple signaling pathways pharmacologically while monitoring the synaptogenic activity of IgSF21 and Nlgn2. Interestingly, both IgSF21 and Nlgn2 require c-jun N-terminal kinase (JNK)-mediated signaling, whereas Nlgn2, but not IgSF21, additionally requires CaMKII and Src kinase activity. JNK inhibition diminished de novo presynaptic differentiation without affecting the maintenance of formed synapses. We further found that Nrxn2α knockout brains exhibit altered synaptic JNK activity in a sex-specific fashion, suggesting functional linkage between Nrxns and JNK. Thus, our study elucidates the structural and functional relationship of IgSF21 with Nrxn2α and distinct signaling pathways for IgSF21-Nrxn2α and Nlgn2-Nrxn synaptic organizing complexes in vitro. We therefore propose a revised hypothesis that Nrxns act as molecular hubs to specify synaptic properties not only through their multiple extracellular ligands but also through distinct intracellular signaling pathways of these ligands.

AFM Imaging Reveals MicroRNA-132 to be a Positive Regulator of Synaptic Functions.

The modification of synaptic and neural connections in adults, including the formation and removal of synapses, depends on activity-dependent synaptic and structural plasticity. MicroRNAs (miRNAs) play crucial roles in regulating these changes by targeting specific genes and regulating their expression. The fact that somatic and dendritic activity in neurons often occurs asynchronously highlights the need for spatial and dynamic regulation of protein synthesis in specific milieu and cellular loci. MicroRNAs, which can show distinct patterns of enrichment, help to establish the localized distribution of plasticity-related proteins. The recent study using atomic force microscopy (AFM)-based nanoscale imaging reveals that the abundance of miRNA(miR)-134 is inversely correlated with the functional activity of dendritic spine structures. However, the miRNAs that are selectively upregulated in potentiated synapses, and which can thereby support prospective changes in synaptic efficacy, remain largely unknown. Using AFM force imaging, significant increases in miR-132 in the dendritic regions abutting functionally-active spines is discovered. This study provides evidence for miR-132 as a novel positive miRNA regulator residing in dendritic shafts, and also suggests that activity-dependent miRNAs localized in distinct sub-compartments of neurons play bi-directional roles in controlling synaptic transmission and synaptic plasticity.

Studies on high power laser cladding Stellite 6 alloy coatings: Metallurgical quality and mechanical performances

The present study systematically investigates the effect of powder feeding rates (Vp) on the quality of Stellite 6 alloy coatings with a 20 kW fiber laser. The results demonstrate that the hot cracks in the Stellite 6 coatings can be effectively eliminated by increasing the Vp without preheating substrate or adding buffer layers. It is possible to achieve a single-track coating with a thickness of 2.34 mm, width of 20 mm and dilution rate of 17.3 % with crack-free and densely microstructure when Vp is 90 g/min. Moreover, the build rate (172 mm3/s) surpasses the maximum build rate (133 mm3/s) of low power laser cladding. The heat accumulation of multi-track and double-layer (5.6 mm) under high power laser results in the formation of ε-Co through phase transformation from part of γ-Co. Consequently, the dendrite region primarily consists of γ-Co while a small amount of ε-Co and Cr23C6 dominate in the inter-dendritic region. Although the heat accumulation effect also tends to coarsen the grains in bottom region of the coatings, leading to a slight reduction in mechanical properties, both hardness (485 HV–523 HV) and tensile strength (1131 MPa–1250 MPa) are comparable to those achieved by low power laser cladding, and the break elongation (6.9 %–8.1 %) has significantly surpassed the current level of 3 %. High power laser cladding processes may play a significant role in enhancing the effectiveness of surface modification or remanufacturing for large workpieces, such as the runner of hydroelectric generator set.

Enhanced wear resistance of a multi-phase reinforced Al0.5CrFeNi2.5Si0.25 high-entropy alloy via annealing

In this work, a multiphase reinforced non-equiatomic Al0.5CrFeNi2.5Si0.25 high-entropy alloy (HEA) was prepared by vacuum induction melting. The effect of heat-treatment temperature (1023, 1123, 1323, and 1473 K) on the microstructure, mechanical properties, and wear behavior are systematically investigated. The results indicate that the as-cast and annealed alloys are composed of face-centered cubic (FCC) and body-centered cubic (BCC) structures accompanied by microscale and nanoscale precipitated phases. To be specific, the FCC matrix is enriched in the L12 phase, and BCC particles and σ phases are observed in the B2 matrix. The microstructure of Al0.5CrFeNi2.5Si0.25 HEAs consists of dendritic region (DR) and inter-dendritic (ID) region before and after annealing. The phases and microstructure did not change. After annealing, the size of the Cr-rich BCC particles is reduced. The L12 phase has a density per unit area that first increases and then decreases, reaching its highest density at 1123 K. With the annealing temperature rising, the nanohardness increases slightly and then decreases, reaching a peak value of about 6.29 GPa at 1123 K. The Al0.5CrFeNi2.5Si0.25 HEA annealed at 1123 K also exhibits the lowest specific wear rate of 2.43 × 10−4 mm3/Nm, which is decreased by 23.5% compared to the as-cast one.

Crystallographic texture and multiscale boundaries mediated creep anisotropy in additively manufactured Ni-based Hastelloy C276 superalloy

The microstructure and high-temperature creep mechanisms of Ni-based Hastelloy C276 superalloy fabricated using wire and arc-based directed energy deposition were investigated systematically and innovatively. The microstructural investigation revealed that the as-fabricated samples comprise γ-Ni matrix and topologically close-packed (TCP) P phase precipitates. The γ matrix subgrains and grains are spread over multiple highly textured columnar dendrites, with a majority of γ <001> crystallographic orientations closely aligned along the deposition direction. Moreover, the interdendritic regions exhibit severe Mo segregation, P phase particles, and dislocation bands. Creep tests were conducted on miniature samples under various temperature and stress conditions, loaded either in the deposition direction (DD) or travel direction (TD). DD samples exhibit lower minimum strain rates, greater strains-to-failure, and longer creep rupture lifetimes than TD samples, indicating significant creep anisotropy. Dislocation creep was identified as the primary creep mechanism for both DD and TD conditions. During creep, dynamic precipitation of TCP phases occurred in the interdendritic regions, resulting in varying creep resistance between interdendritic and dendritic core regions. Isostress and isostrain models, considering both crystallographic texture and precipitation strengthening, reasonably predicted the observed creep anisotropy during the secondary creep stage. Additionally, variations in the Schmid factor led to significant deformation incompatibility among dendrites in TD samples. Dislocation accumulation in TD sample interdendritic regions promoted new grain nucleation, triggering dynamic recrystallisation, facilitating grain boundary sliding, and accelerating tertiary creep. Furthermore, TCP phase particles in the interdendritic regions contributed to microcrack development, further accelerating creep fracture, especially in the TD condition.

Surveying the Effects of Aging a High C-Containing Co-Based Superalloy From the As-Cast and Solution Heat-Treated Conditions

The microstructure of the high carbon-containing cobalt-based superalloy, Co-101, has been studied in the as-cast state and following a variety of heat treatments. In the as-cast state both M7C3 and Mo-rich M23C6 carbides were observed in the interdendritic regions. After thermal exposure at temperatures between 1000 °C and 1250 °C for 1, 10, and 100 hours, the M7C3 interdendritic carbide network was observed to transform into a Mo-lean M23C6 carbide. These changes were rationalized with thermodynamic calculations. The carbide transformation liberated carbide-forming elements that resulted in the precipitation of intragranular carbides in the dendritic regions at temperatures below 1150 °C. These carbides in the cast-aged material preferentially formed at the dendrite peripheries early during exposure, leading to wide particle size distributions. Peak hardness in the cast-aged material was attained within the first 10 hours of exposure and softening was observed thereafter. After solution heat treating at 1250 °C for 10 hours, the microstructure of Co-101 comprised an M23C6 interdendritic carbide network and solid solution dendrites supersaturated with carbide-forming elements. Subsequent aging of this microstructure for 100 hours at 900 °C led to a high number density and narrow particle size distribution of intragranular carbides. The characteristics of these carbides in the solution-aged material resulted in greater hardness, which was retained for longer durations of exposure, than the cast-aged specimens.

Physical and functional convergence of the autism risk genes Scn2a and Ank2 in neocortical pyramidal cell dendrites

Dysfunction in sodium channels and their ankyrin scaffolding partners have both been implicated in neurodevelopmental disorders, including autism spectrum disorder (ASD). In particular, the genes SCN2A, which encodes the sodium channel NaV1.2, and ANK2, which encodes ankyrin-B, have strong ASD association. Recent studies indicate that ASD-associated haploinsufficiency in Scn2a impairs dendritic excitability and synaptic function in neocortical pyramidal cells, but how NaV1.2 is anchored within dendritic regions is unknown. Here, we show that ankyrin-B is essential for scaffolding NaV1.2 to the dendritic membrane of mouse neocortical neurons and that haploinsufficiency of Ank2 phenocopies intrinsic dendritic excitability and synaptic deficits observed in Scn2a+/- conditions. These results establish a direct, convergent link between two major ASD risk genes and reinforce an emerging framework suggesting that neocortical pyramidal cell dendritic dysfunction can contribute to neurodevelopmental disorder pathophysiology.

Combustion-synthesised TiAl/NiAl layered intermetallic composite: synthesis, phase composition, and microstructure

ABSTRACT The joining of different intermetallics (e.g. NiAl, TiAl) is important for high-temperature applications. In this study, self-propagating high-temperature synthesis was used for simultaneous joining of (Ni+Al) and (Ti+Al) layered samples of the stoichiometric compositions. The main advantage of such joining by self-propagating high-temperature synthesis is that it could be done at ambient temperature without the use of a furnace. The applied load during combustion synthesis was used to improve the contact between the Ni-Al and Ti-Al layers. The obtained results demonstrate that TiAl/NiAl intermetallics were successfully joined together with a bonding interface of about 170 μm thickness. XRD analysis has shown that the joining area consists of NiAl, TiAl, Ti3Al, and NiTiAl2 phases. The SEM data analysis of the transition zone of NiAl-TiAl conjunction has revealed that the transition zone consists of several intermediate layers: a polycrystalline NiAl layer; an intermediate layer based on Ni-Al-Ti containing NiTiAl2 phase; a layer based on Ni-Al-Ti with mixed dendritic and eutectic regions; and a polycrystalline TiAl layer.The measured microhardness of the transition zone varies from 3200 up to 13,600 MPa with the maximum microhardness of 1355 ± 45 MPa corresponding to the layer identified as the NiTiAl2 phase.

Effect of non-metallic silicon content on the microstructure and corrosion behaviour of AlCoCrFeNi high-entropy alloys

AlCoCrFeNi high-entropy alloys (HEAs) have shown excellent mechanical properties and high-temperature oxidation resistance but poor corrosion resistance owing to the high contents of the aluminium passivation film. In this study, Si was added to these alloys with the aim of improving the composition and stability of the passivation films. The microstructure and corrosion behaviour of AlCoCrFeNiSix (molar ratio x = 0, 0.1, 0.2, 0.3, and 0.4) HEAs were investigated. Dendritic and spinodal decomposition regions were observed in all five alloys. In the dendritic region, the dendritic structures transitioned from a petal shape to a dendritic shape with increasing Si content. Phase separation occurred in the spinodal decomposition region, which predominantly consisted of ordered body-centred cubic (B2) and disordered body-centred cubic (A2) phases. The size of the A2 phase decreased, and the amount of the A2 phase increased with increasing Si content. An optimised Si content could enhance the stability of Al and Cr passivation films, whereas excessive Si imposed an adverse effect by forming a Cr passivation film. The corrosion resistance of AlCoCrFeNiSi0.2 HEAs was optimum with a passive current density of 3.2 μA/cm2, which was 0.2 times that of the obtained AlCoCrFeNi HEAs without Si. The type of corrosion changed from local corrosion of AlCoCrFeNiSix (x ≤ 0.3) HEAs to general corrosion of AlCoCrFeNiSi0.4 HEAs. The corrosion mechanisms of the AlCoCrFeNi HEAs with various Si contents were elucidated.

Pitting corrosion mechanism of BCC+FCC dual-phase structured laser cladding FeCoCrNiAl0.5Ti0.5 HEAs coating

This work elaborated the microstructure and corrosion behaviors of laser cladding (LC) FeCoCrNiAl0.5Ti0.5 high-entropy alloys (HEAs) coating on AISI 1045 steel substrate. It revealed that the LC FeCoCrNiAl0.5Ti0.5 HEAs coatings were composed of dendritic region (DR) and interdendritic region (IR). Furthermore, DR was mainly composed of BCC phase while IR was composed of FCC phase. There was also the transformation of BCC to L21 structure detected due to the addition of Ti element. Due to the uniform microstructure and addition of corrosion-resistant elements (such as Cr), the dual-phase HEAs coatings exhibited pretty good corrosion resistance. A dense passive film would form during the corrosion process to protect the inner structure. It was demonstrated that the corrosion rate of the coating was only 32.8% of that of the substrate. However, the pores formed during the LC process on the surface might be the initial site for pitting corrosion.

Microstructures Evolution of a Second Generation Single Crystal Superalloy after Long Term Aging at 980°C

The microstructure evolution of the second-generation single crystal superalloy DD412 aged at 980°C for 1000 h were investigated. The results show that needle-shaped topologically close packed (TCP) phases rich in Re and W were firstly found in the dendritic core region after aging at 980°C for 400h, while the size and amount of TCP phases increased gradually with aging time, which is due to the fact that high melt point elements Re and W segregated to the dendritic core region. With the increment of aging time, the size of γ′ phase increased and volume fraction of γ′ phase decreased. The γ′ phase in dendrite core and inter-dendrite region remained cuboidal basically, and the γ′ phase in second dendritic arm showed directional coarsening after aging for 800 h. The MC carbides in inter-dendritic region decomposed gradually and transformed to the M6C carbides partially during long term aging, while few fine blocky M6C carbides precipitated in dendritic core after aging for 400h. The different microstructure evolution in dendritic region is due to the dendrite segregation of alloying elements and elements diffusion during aging.

Cell-Type Specific Connectivity of Whisker-Related Sensory and Motor Cortical Input to Dorsal Striatum.

The anterior dorsolateral striatum (DLS) is heavily innervated by convergent excitatory projections from the primary motor (M1) and sensory cortex (S1) and considered an important site of sensorimotor integration. M1 and S1 corticostriatal synapses have functional differences in their connection strength with striatal spiny projection neurons (SPNs) and fast-spiking interneurons (FSIs) in the DLS and, as a result, exert distinct influences on sensory-guided behaviors. In the present study, we tested whether M1 and S1 inputs exhibit differences in the subcellular anatomical distribution of striatal neurons. We injected adeno-associated viral vectors encoding spaghetti monster fluorescent proteins (sm.FPs) into M1 and S1 in male and female mice and used confocal microscopy to generate 3D reconstructions of corticostriatal inputs to single identified SPNs and FSIs obtained through ex vivo patch clamp electrophysiology. We found that M1 and S1 dually innervate SPNs and FSIs; however, there is a consistent bias towards the M1 input in SPNs that is not found in FSIs. In addition, M1 and S1 inputs were distributed similarly across the proximal, medial, and distal regions of SPN and FSI dendrites. Notably, closely localized M1 and S1 clusters of inputs were more prevalent in SPNs than FSIs, suggesting that cortical inputs are integrated through cell-type specific mechanisms. Our results suggest that the stronger functional connectivity from M1 to SPNs compared to S1, as previously observed, is due to a higher quantity of synaptic inputs. Our results have implications for how sensorimotor integration is performed in the striatum through cell-specific differences in corticostriatal connections.